Bio 201 1st Edition Lecture 31Outline of Last Lecture I. Fredrick GriffithII. VirusesA. The Hershey-Chase Experiment Outline of Current LectureI. How Is DNA Replicated?A. Differential CentrifugationB. Density Gradient CentrifugationC. Meselson and Stahl ExperimentCurrent LectureI. How is DNA Replicated? -3 possible options. 1) Semi-conservatively- Each daughter cell inherits 1 parent cell 2) Conservative- One daughter cell gets both parent cells and other daughter is a copy of daughter 1. 3) Dispersive- Random inheritance. A. Differential Centrifugation- Particles whose mass> specific threshold pellet at selected centrifugal force. Separated based on size, good for separation of structures with very different masses. B. Density Gradient Centrifugation- Separates based on density, better than differential centrifugation. Suspension is a solute concentration gradient. All particles settle at location where solute= particle density. This is better for separation of similarly sized things, requires high speeds and special equipment. II. Meselson and Stahl Experiment- 1958, used density gradient centrifugation to separate newly synthesized DNA from original DNA to reveal the mechanism of replication. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-In this experiment, they extracted DNA and placed it in a tube with CsCl gradient, thenthey centrifuged the tube and observed it with UV light. Next, the incorporated N15 into DNA. They fed e. coli only N15 for several generations, they purified DNA from N15-fed bacteria and compared it to DNA from bacteria N14-only fed. They placed both N15 and N14 DNA into one tube and centrifuged it. They replaced N15 with N14 checking up after each new generation. The parental DNA remains, the longer its grown the more N14 DNA shows.-RESULT: DNA replication is semi-conservative. During cell division, each daughter cell inherits one old strand of parental DNA and one new
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